An electrospray ion source for magnetic sector mass spectrometers

Electro spray mass spectra of carbonic anhydrase (MW ～ 29000) and ovalbumin (MW ～ 45000) were obtained on a double focusing magnetic secter mass spectrometer by using a single stage of mechanical pumping in the interface between atmospheric pressure and high vacuum. Full scan spectra of lysozyme were recorded on 15 fmoles consumed. In addition, accurate mass measurement was demonstrated for peptides and proteins, and resolution in excess of 10,000 (m /△m, 10% valley) was observed. These results clearly show that high performance magnetic sector mass spectrometers can be advantageously interfaced to an atmospheric pressure electrospray ion source.     

Electron-capture negative ionization calibrants for magnetic sector mass spectrometers

Fomblin [poly(perfluoropropylene oxide)], PFK (perfluorokerosene) and FC-43 (perfluorotributylamine) are investigated as mass calibrants in electron-capture negative ionization mass spectrometry on a magnetic sector hybrod mass spectrometer. This work provides exact negative ion mass tables of these three calibrants obtained using high-resolution peak matching of representative ions of the calibrants against ions of known mass. The suitability of these calibrants for full data system control in the negative ionization mode is demonstrated for the techniques of high-resolution scanning, selected ion recording and calibration of the quadrupole sector of a hybrid instrument.     

Linear time-of-flight mass spectrometers: Postsource pulse focusing conditions and mass scale

The condition to cancel aberrations that result from initial ion velocities and length of ionization process by postsource pulse focusing in linear time-of-flight mass spectrometers is derived. The ion arrival time distribution as a function of ion mass is given, which permits mass scale calibration. Simple formulas allow calculation of the voltage needed for postsource pulse focusing and the limits of the mass range where the focusing action is felt. The theory is illustrated for a specific instrument case.     

Electron ionization mass spectra of indolenines obtained using sector and ion trap mass spectrometers

The electron impact (EI)-induced fragmentations of 18 indolenines were studied using both double-focusing and ion trap mass spectrometers. The compounds used in this study were synthesized to provide correlations of characteristic fragment ions with specific structural differences. In 2-hydroxyindolenines the hydroxy group was involved in a major fragmentation process by interacting with the ester side chain to generate an alpha,beta-unsaturated gamma-lactone structure, with concomitant loss of the corresponding alcohol. In contrast, loss of an alkyl radical, derived solely from the 2-alkoxy group, is a major primary decomposition process for 2-alkoxyindolenines. EI-MS analyses using sector and ion trap spectrometers resulted in similar fragmentation patterns.     

Scanning of sector mass spectrometers to observe the fragmentations of metastable ions

Various methods of scanning the electric and the magnetic sectors of a double focusing mass spectrometer are critically discussed and assessed.     

Hybrid mass spectrometers for tandem mass spectrometry

Mass spectrometers that use different types of analyzers for the first and second stages of mass analysis in tandem mass spectrometry (MS/MS) experiments are often referred to as "hybrid" mass spectrometers. The general goal in the design of a hybrid instrument is to combine different performance characteristics offered by various types of analyzers into one mass spectrometer. These performance characteristics may include mass resolving power, the ion kinetic energy for collision-induced dissociation, and speed of analysis. This paper provides a review of the development of hybrid instruments over the last 30 years for analytical applications.     

Parent ion resolution in linked scans for dissociations occurring in the first field-free region of sector mass spectrometers

A frequently employed means of studying reactions of ions under high energy collisional activation conditions involves linked scanning a double-focusing mass spectrometer to detect product ions formed in the first field-free region. Experiments have demonstrated that the effective resolution of the parent ion varies during the course of a product ion scan, and this variation is attributed to the kinetic energy released during dissociation. Carefully generated Lacey-Macdonald ion intensity diagrams accurately reflect the dissociation events occurring in various regions of sector mass spectrometers. Consideration of such diagrams leads to an understanding of the noted phenomena and allows the derivation of an expression for the effective parent ion resolution. Furthermore, the approach predicts that parent ion resolution varies during constant neutral loss scans and that the relatively poor resolution (and its variation) can provide particularly misleading data. Results from product ion scans with stable isotope-labeled compounds and constant neutral loss scans with rubidium bromide and stable isotope-labeled peptide derivatives were consistent with the theoretical predictions     

Analyzer scan modes for hybrid mass spectrometers

The scan modes that can be used to obtain daughter ion, parent ion, and constant neutral-loss spectra on hybrid mass spectrometers are derived for instruments with a quadrupole combined with a magnetic and/or electric sector. All combinations of sector/quadrupole and quadrupole/sector instruments are discussed. The advantages or lack thereof of the various scans are presented with respect to operation, resolution and potential artifacts.     

Direct sampling time-of-flight mass spectrometers for technological analysis

The practicability of direct sampling time-of-flight mass spectrometers for routine technological analysis is considered. The discussed set incorporates two TOF instruments together covering analysis of solid, liquid, and gas samples without the need for time consuming sample preparation. Both an electron ionization reflectron TOF mass analyzer designed for the analysis of gas and liquid samples and a laser ionization axial electrostatic TOF mass analyzer designed for analysis of solid and powder samples use a single system for data acquisition, collection and processing. These instruments achieve ng/g range sensitivity and mass resolution exceeding 1000. Because of its compact design the system also can be realized as a mobile laboratory for on-site analysis. Prospects for applying the instruments to different technological applications are discussed. Received: 17 July 1997 / Revised: 28 November 1997 / Accepted: 22 December 1997     

Direct sampling time-of-flight mass spectrometers for technological analysis

The practicability of direct sampling time-of-flight mass spectrometers for routine technological analysis is considered. The discussed set incorporates two TOF instruments together covering analysis of solid, liquid, and gas samples without the need for time consuming sample preparation. Both an electron ionization reflectron TOF mass analyzer designed for the analysis of gas and liquid samples and a laser ionization axial electrostatic TOF mass analyzer designed for analysis of solid and powder samples use a single system for data acquisition, collection and processing. These instruments achieve ng/g range sensitivity and mass resolution exceeding 1000. Because of its compact design the system also can be realized as a mobile laboratory for on-site analysis. Prospects for applying the instruments to different technological applications are discussed. Received: 17 July 1997 / Revised: 28 November 1997 / Accepted: 22 December 1997     

Modern Russian mass spectrometers for the atomic industry

Product quality control within the nuclear fuel cycle is a subject of special concern in Russia nowadays. Earlier, mass spectrometers of foreign production were commonly used for elemental and isotope analysis of samples. Currently, a series of domestic mass spectrometers MTI-350 has been developed and their production has been organized in Russia. The series comprises an automated MTI-350G mass spectrometer for the isotope analysis of uranium hexafluoride; thermal ionization MTI-350T mass spectrometer for the isotope analysis of uranium, plutonium, and mixed oxide (MOX) fuels; an MTI-350GS mass spectrometer for controlling the production of uranium hexafluoride; and an MTI-350GP mass spectrometer for the determination of the impurity concentration in uranium hexafluoride. The article considers operation principles, analytical characteristics, and the advantages of the above mass spectrometers.     

Prediction of artifact peak intensity in linked scans for dissociations occurring in the first field-free region of sector mass spectrometers

Linked scans are commonly used on double-focusing mass spectrometers to obtain tandem mass spectrometry (MS/MS) spectra. The appearance of artifact peaks in linked scan MS/MS spectra from dissociations occurring in the first field-free region are a result of poor parent ion resolution, and they often can complicate the interpretation of the MS/MS spectra. The kinetic energy release associated with dissociation of ions of similar m/z to the “selected” parent ion is the main factor in determining the intensity of artifact peaks. A means of predicting the intensities of these artifact peaks in product ion and constant neutral loss scans is presented here. The method requires straightforward calculations based on Lacey-Macdonaldion intensity diagrams. The exact calculations require knowledge of the kinetic energy release of a particular dissociation, the kinetic energy spread of the main beam, and the parent ion and product ion mass-to-charge ratios. Adequate predictions, however, can be made by assuming a general kinetic energy release for any given reaction and a typical instrument energy resolution. Theoretical predictions are in good agreement with experimental data obtained from the product ion scans of unlabeled and isotopically labeled tirilazad and unlabeled and labeled leucine enkephalin methyl ester. There is also excellent agreement between experiment and theory in the constant neutral loss scans of rubidium bromide clusters.     

A new linked scan for reversed geometry mass spectrometers

A new linked scan is described by which fragmentations occurring in the second field free region of a two sector instrument can be monitored. The scan can be used only if the first stage allows selection of ions according to their masses. The magnetic sector and electric sector are scanned in unison so that the product B²E is maintained constant. A spectrum of all parents of a preselected daughter ion is obtained and the resolution depends only on the mass resolution of the magnetic sector.     

A pulsed-leak valve for use with ion trapping mass spectrometers

A pulsed-leak valve that allows the introduction of a prolonged, flat, and controllable pulse of gas is described. Test results from the valve that utilized a Fourier transform ion cyclotron resonance mass spectrometer with Ar and C₂H₆ as the sample gases indicate that the valve functions as expected and yields basically rectangular pressure profiles in the cell region. The rise and fall times are similar to those of just the stand-alone pulsed valve and are believed to be determined mainly by the design of the vacuum system, rather than the design of the pulsed-leak valve. Kinetic data for the reaction of Nb⁺ with C₂H₆, acquired with the use of the pulsed-leak valve to introduce the C₂H₆ gas, demonstrates the practical application of this valve for kinetic and other analogous studies. Use of the pulsed-leak valve greatly reduces the loss of the reactant ion signal during the cooling period.     

Glow discharge electron impact ionization source for miniature mass spectrometers

A glow discharge electron impact ionization (GDEI) source was developed for operation using air as the support gas. An alternative to the use of thermoemission from a resistively heated filament electron source for miniature mass spectrometers, the GDEI source is shown to have advantages of long lifetime under high-pressure operation and low power consumption. The GDEI source was characterized using our laboratory's handheld mass spectrometer, the Mini 10. The effects of the discharge voltage and pressure were investigated. Design considerations are illustrated with calculations. Performance is demonstrated in a set of experimental tests. The results show that the low power requirements, mechanical ruggedness, and quality of the data produced using the small glow discharge ion source make it well-suited for use with a portable handheld mass spectrometer.     

Field-deployed underwater mass spectrometers for investigations of transient chemical systems

The mass spectrometer developments and underwater deployments described in this work are directed toward observations of important reactive and influential inorganic and organic chemicals. Mass spectrometer systems for measurement of dissolved gases and volatile hydrocarbons were created by coupling a membrane analyte-introduction system with linear quadrupole and ion trap mass analyzers. For molecular masses up to 100 amu, the in situ quadrupole system has detection limits on the order of 1-5 ppb. For masses up to approximately 300 amu, the underwater ion trap system detects many volatile hydrocarbons at concentrations below 1 ppb. Both instruments can function autonomously or via interactive communications from a remote control site. Continuous operations can be sustained for up to approximately 12 days. Deployments have initially involved shallow water proof-of-concept operations at depths less than 30 m. Future modifications are planned that will allow operational depths to 200 m.